Mutations that cause renal cystic disease provide powerful tools to identify the molecular determinants of renal cyst formation. In humans, genetic cystic kidney diseases are inherited as simple mendelian traits, exhibit wide variability in phenotype and account for approximately 10% of end stage renal disease in both adult and pediatric populations. Linkage studies that mutations in several distinct loci cause renal cystogenesis. yet, only some of the human loci have been mapped and to date none have cloned. The mouse provides an excellent experimental model to identify molecular determinants of renal cyst formation. In the mouse, several cystic kidney mutations have been described each disrupts a distinct gene and the mutant phenotypes closely resemble human diseases. Of these models, the congenital polycystic kidney (cpk) mutation is best characterized. Based on microdissection and cell biology data, we hypothesize that cpk is an important molecular determinant of both cystogenesis and the terminal differentiation of renal tubular epithelia. As the first step in a positional cloning strategy, my laboratory has mapped cpk to proximal mouse Chromosome 12. Of note, no recombination events were detected between cpk and D12Nyu2. Our genetic map: centromere-(Odc,D12Mit10)-(cpk,D12Nyu2)-(Tpo,D12Mit 12)-telomere, positions cpk within a 1.3 cM region centered on D12Nyu2. Based on this map, we will establish the molecular framework required to clone the cpk gene. The goals of this proposal are to: 1) construct a physical map of the chromosomal region centered on cpk using the techniques of pulsed field gel electrophoresis (PFGE) and yeast artificial chromosome (YAC) cloning; 2) identify candidate cpk cDNAs using the complementary strategies of HTF island identification, YAC- based cDNA selection and mRNA differential display and 3) characterize the candidate cpk cDNAs. Once the cpk gene is cloned, future studies will be directed at 1) functionally characterizing the molecular defect in this well-defined mouse model of PKD; and 2) determining the relationship between renal tubular cyst formation and renal tubular differentiation. In light of the extensive genetic conservation between mice and humans, we will also use the cpk gene to identify its human homolog and determine the role of this human gene in renal cystic disease.